The Morse code

Chapter The Morse code

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • The Morse codeThe simplest, and oldest, form of modulation is on-off keying. Early telegraph systemsused direct currents that were keyed on and off, and were sent along wires. The first ra-dio transmitters employed spark-generated “hash” signals that were keyed using thetelegraph code. The noise from the sparks, like ignition noise from a car, could be heardin crystal-set receivers several miles away. At the time of their invention, this phenom-enon was deemed miraculous: a wireless telegraph!Keying is usually accomplished at the oscillator of a continuous-wave (CW) radiotransmitter. A block diagram of a simple CW transmitter is shown in Fig. 26-1. This isthe basis for a mode of communications that is, and always has been, popular among ra-dio amateurs and experimenters.Frequency-shift keying47526-1A simple CW transmitter.While the use of Morse code might seem old-fashioned, even archaic, a CW trans-mitter is extremely simple to build. A human operator, listening to Morse code and writ-ing down the characters as they are sent, is one of the most efficient data receivers everdevised. Until computers are built to have intuition, there’ll always be a place for Morsecode radio communications. Besides being efficient, as any “CW fanatic” radio ham willtell you, it’s just plain fun to send and receive signals in Morse code.Morse code is a form of digital communications. It can be broken down into bits,each having a length of one dot. A dash is three bits long. The space between dots anddashes, within a single character, is one bit. The space between characters in a word isthree bits. The space between words is seven bits. Punctuation marks are sent as char-acters attached to their respective words. An amplitude-versus-time rendition of theMorse word “eat” is shown in Fig. 26-2.Morse code is a rather slow way to send and receive data. Human operators typi-cally use speeds ranging from about 5 words per minute (wpm) to 40 or 50 wpm.Frequency-shift keyingMorse code keying is the most primitive form of amplitude modulation (AM). Thestrength, or amplitude, of the signal is varied between two extreme conditions: full-onand full-off. There is another way to achieve two-state keying that works better with